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The Acoustics of the Roman Theatre in Benevento
Gino Iannace, Amelia Trematerra, Giuseppe Ciaburro
To cite this version:
THE ACOUSTICS OF THE ROMAN THEATRE IN
BENEVENTO
Giuseppe Ciaburro
1Gino Iannace
1Amelia Trematerra
11 Department of Architecture and Industrial Design, Università della Campania Luigi Vanvitelli, Borgo San Lorenzo,
81031 Aversa, Italy
Correspondence gino.iannace@unicampania.it
ABSTRACT
Thousands theatres during the Hellenistic period in Greece and in its overseas colonies and during the period of Imperial Rome were built. The theatres were built to entertain people and create venues for shows. The theatres have three principal elements the stage (actor position), the orchestra and the cavea (spectator seating). The Greek and Roman theatres differ in constructive elements, but in any case they were without a ceiling, in the open air. The theatres were abandoned afterwards the barbarian invasions and during the Middle Ages they were turned into houses, into fortresses or used to take materials to build buildings. So the theatres were forgotten for many centuries. In the Renaissance period the theatres were rediscovered and studied. Today ancient theatres are the heart of city events and are used for various kinds of shows. This paper reports the acoustic characteristics of the Roman theatre in Benevento evaluated in different listening points in the cavea. The theatre was built in the second century A.D, it was destroyed after the barbaric invasion. The theatre was renovated in the first half of the 1900s. Today the theatre is the center of important social and cultural activities. Acoustic measurements inside the theatre were taken by placing an omnidirectional sound source on the stage and in the orchestra, with the microphones in the cavea along three directions. The acoustic characteristics in the various seating areas were evaluated. It possible to understand in which sectors of the cavea the acoustic conditions are optimal for listening to different types of theatrical performances.
1. INTRODUCTION
Thousands theatres during the Hellenistic period in Greece and in its overseas colonies and during the period of Imperial Rome were built. The theatres were built to entertain people and create venues for shows. During the Imperial Roman age thousands of theatres were built throughout the whole empire (Jordan, Turkey, Libya, France, Italy, Spain, Germany, Greece). The best preserved are in Jordan and Turkey, but there are also examples in Italy, Spain and France. The first theaters built in Greece were resting on the slope of a hill and had a structure with linear steps. Over time it was built to a concentric stepped structure, this configuration in addition to improving the vision, allowed a more optimal sound distribution, so the legend of the good acoustics of the Greek theaters was born. The theatres admired nowadays
are often not a very faithful reconstruction of the original ones. How the theatres had to be built is described by Vitruvius (first century B.C.), in the “De Architectura”. In the 5th book, the fundamental principles for achieving a correct vision and listening of the theatrical performances are introduced [1, 2], Figure 1 shows the theatre principal elements (scaena, orchestra, cavea). Benevento (south of Italy) was an important Roman city during the Imperial Age. The theatre was built in the second century A.D., made up of 25 arcades on three levels; the orchestra with 10 m radius, the cavea with 40 m radius. The scaena (pit stage) was probably made up of two orders of columns with a sloped wooden roof. The cavea (the area of the theatre where spectators sit) could contain over 10,000 spectators [3, 4, 5]. The “ima cavea” is leaned onto two semi-circular ambulacra, each connected through corridors alternated with staircases that lead to the upper part. The theatre had also a summa cavea. When the theatre was built, the tragedy was an exhausted theatrical genre by that time, so the theatre represented the symbol of the greatness of the city, public meetings took place inside it and the shows were comedies and satirical representations [6]. Figure 2 shows the Roman theatre in a virtual reconstruction
Figure 1. Theatre principal elements.
day more bearable and to mitigate the acrid odors of the crowd.
Figure 2. Roman theatre in a virtual reconstruction.
Figure 3. Position of the “velaria” over the cavea.
Figure 4. Virtual reconstruction of the theatre for acoustic
simulations.
Figure 4 shows the virtual reconstruction of the theatre for acoustic simulations. The virtual model was created through the use of a 3D software cad and it was imported into the software for architectural acoustic, the analysis is performed with ray-tracing technique. The virtual model requires knowledge of the acoustic properties of the
surfaces which made up the theatre. In this case the absorption coefficient is very low because the theatre’s materials are acoustically hard (marble). The average value simulated of STI=0.6 corresponds to a good value of speech intelligibility. The average values simulated of reverberation time do not exceed 2.0 seconds, which is a result similar to the studies carried out by other authors for other ancient theatres [7]. This value indicates that in the Roman theatre the speech reception was good, and the actor’s voice was clearly heard and understood by the spectator. If the public kept silent or paid attention to theatrical plays, it was due to the actor’s ability to “tame" and involve the crowd. With the advent of Christianity and after the barbaric invasion, the theatre was abandoned, and the following earthquakes, floods and lootings led to its destruction. During the centuries, some houses were built inside on the cavea and in the 18th century, on the right side of the cavea, the church was built, using the structure of the theatre as substratum. The church is still used today for sacred services.
Figure 5. Painting of the XVIII century, representing the
rests of the Roman theatre.
Figure 6. Picture of the beginning of the 1900s. The
houses inside the cavea of the theatre.
Figure 7. Stage (scaena) and orchestra.
Figure 8. Cavea, orchestra and stage (scaena).
Figure 9. Aerial view.
Figure 10. Orchestra and cavea during a show in the
summer season.
Figure 6 shows a photo of the early 1900 in which the houses placed inside the theatre are visible. The houses
built in the cavea were demolished in 1930 so as to rebuild the cavea and a part of the stage building. Only the church, over a part of the cavea, has survived. Nowadays the Roman theatre is struck by the red colour of the bricks covering the cavea, but in the Imperial age, it was covered with white marble and the stage building was adorned with columns and marbles. The “ima cavea” was rebuilt with terracotta bricks with fifteen steps, a height of 0.40 m and depth of 0.70 m, while the “summa cavea” was only partially rebuilt and cannot be accessed by spectators. The theatre began to be used for events from the 1950s. Today, the theatre is used for different types of shows: opera, drama, dance as well as symphonic, jazz and pop concerts. During the annual national cultural meeting as “Benevento
città spettacolo”, the theatre becomes the centre of the
most important performances including comedy, drama and musical shows, with the maximum capacity being about 1,800 spectators. Figure 7, Figure 8 and Figure 9 shows the internal view of the theatre in actual state. While Figure 10 shows the orchestra and stage during a show in the summer season.
2. ACOUSTIC MEASUREMENTS
The acoustic measurements gives information about the acoustic characteristics of the theatre. When the actors are on stage or the musicians are in the orchestra. In order to obtain this information, a spherical sound source was first placed on the stage and then in the orchestra. The sound is detected through a microphone set in the cavea staircases at constant distance in three radial directions. The sound emitted by the sound source interacts with the surfaces of the theatre and is then detected by the microphone set in the cavea. The sound detected by the microphone is the composition of the direct component, that means the one let out by the source and that directly reaches the microphone, and the one of the reflected components, that means the components of the sound that are reflected by the surfaces of the theatre before they reach the microphone. The sound source used to carry out the acoustic measurements consisted of an omnidirectional sound source. MLS signals of order 16 with a length of 5 seconds were generated by a 01 dB Symphonie system. The impulse responses were detected by a microphone type GRAS 40 AR ½”. The sound source height from the floor was 1.60 m from the floor. Figure 11 shows the omnidirectional sound source in the orchestra during the acoustic measurements. The microphones were placed on the steps of the cavea, at a height of 0.8 m, with a fixed pitch along three radial directions, one central and two laterals, in order to obtain the average spatial values of the acoustic characteristics of the theatre. The acoustic measurements were carried out with the method of the impulse response, the monaural acoustic parameters analysed in accordance with the ISO 3382 (8). Such as the reverberation time (T30), the Early Delay Time (EDT), the
sound pressure level (Lp), the clarity (C80), the definition
(D50), and the sound transmission index for speech
orchestra) and the positions of the twelve receivers in the cavea along three radial directions. The theatre is an open-air space, so the evaluation of the room criteria which assess the delay of sound reflections is partially valid, since the absence of the ceiling and lateral walls; the acoustic field is more similar to a free field rather than a closed room. In room acoustic evaluations, clarity represents the degree to which different reflections arrives and are perceived by the listener, and it is assessed as an early-to-late arriving sound energy ratio.
Figure 11. Omnidirectional sound source in the orchestra
during the acoustic measurements.
This ratio can be calculated for 80 ms early time limit. The definition considers the early arriving sound energy over the overall sound energy and, similarly to the clarity, it can be calculated for 50 ms early time limit. The acoustic procedure and post processing methodology were similar to those used in other spaces, such as the large theatre (9, 10, 11). While Table 1 reports the optimal values of the acoustic parameters in different musical listening conditions or speech intelligibility.
Parameters EDT, s T30, s C80, dB D50 Values for musical performanc es 1.8 < EDT < 2.6 1.6 < T30 < 2.2 -2 < C80 < 2 < 0.5 Values for speech performanc es 1.0 0.8 < T30 < 1.2 > 0.5
Table 1. Optimal values of the acoustic parameters in
different musical listening conditions or speech intelligibility.
Referred to the position of the sound source in the orchestra and on the stage, Figure 13 shows the average measured values of T30; Figure 14 shows the average
measured values of EDT; Figure 15 shows the average measured values of C80; Figure 16 shows the average
measured values of D50. The average values are reported
in the octave band frequencies from 125 Hz to 4.0 kHz. The standard deviation are reported up for the sound source on the stage (quadrate) and down for sound source in the orchestra (triangle). The average values shown are the synthesis of the twelve measurements obtained in the cavea along the three directions as shown in Figure 12.
Figure 12. Positions of sound source (stage and orchestra)
and the twelve positions of the receivers in the cavea.
3. DISCUSSION
The acoustic measurements confirm that the present lack of a roof, lateral walls, and scene wall, led to reduced sound reflections with small reverberation, as highlighted by the values always below 1.0 second of the T30. Infact,
the voice of the actors or singers arrives weak on the steps, lacking the reinforcement of the reflection of the stage wall and other typical of closed theatres.
Figure 13. Average measured values of T30 .
Figure 15. Average measured values of C80 .
Figure 16. Average measured values of D50 .
With the source in the orchestra, the results of the reverberation time were slightly lower, but overall the acoustic parameters did not change significantly. EDT parameter (Figure 14) is very small due to the absence of reflective surfaces (the rear stage wall and any reflective or diffusing surface are missing). For musical performances is considered the parameter C80 (Figure 15), it is very far from the values for the good understanding of the musical performances. The parameter D50 (Figure 16)
is over 0.8, so in accordance to Table 1 the theatre has good characteristics for the for speech performances. Since the theatre is open (without roof), the change in the sound pressure level (Lp) with the distance from the source position is of particular importance. For the position of the sound source on the stage Figures 17, 18, 19 and 20 show respectively the C80 values measured for the first, fourth,
eighth and twelfth rows. The C80 values are reported for
each row and for three different directions. The measured values are reported for the left, central and right rows. The theatre has insufficient acoustic conditions for performing events such as opera or speech alone. The singer's voice cannot be appreciated by the spectators sitting in the cavea. Furthermore this effect becomes even more negative due to the distance between the cavea and the stage for the presence between these two elements of the orchestra. in fact the spectators, seated in the last rows, complain of a low strength in the singers' voice during the opera. For a good understanding of speech it would not be wrong to use a sound amplification system.
Figures 17. C80 values for the first row.
Figures 18. C80 values for the fourth row.
Figures 19. C80 values for the eighth row.
Figures 21. D50 values for the first row.
Figures 22. D50 values for the fourth row.
Figures 23. D50 values for the eighth row.
The D50 values are near to the unit value (good value for
speech performances), while the C80 varies from 0 dB to
25 dB. Only the first row of the cavea area presents optimal listening conditions for music. The average values of STI =0.81 when sound source was on the pit and STI=0.84 when sound source was in the orchestra, This values confirm an high value for the direct sound components. But one of the advantages of the theatre is the fact that although it is located in the heart of the city it is far from the traffic lines, so background noise levels inside the theatre are very low. For the position of the sound source on the stage, Figures 21, 22, 23 and 24 show respectively the D50 values for the first, fourth, eighth and twelfth row
respectively. The measured values are reported for the left, central and right rows. The D50 values are reported for each
row and for three different directions and are different between them. The theatre, in the actual configuration, does not have symmetrical geometric structures, the walls of the stage are only partly reconstructed, and in the central area, there is no stage wall. The cavea has not been rebuilt, and on the right upper part is occupied by the church built in the Middle Ages, “Santa Maria della Verità”. All these non-symmetrical surfaces help to obtain different values for each radial measurement direction.
Figures 24. D50 values for the twelfth row.
Figure 25. Trend of sound pressure level with the distance
when the sound source is placed on the stage.
Figure 26. Trend of sound pressure level with the distance
when the sound source is placed in the orchestra.
right direction is lower than the other directions. While the change in the sound pressure level is greater along the left direction. When the sound source is placed in the orchestra, Figure 26, there is an inversion of the values of the sound pressure level (Lp). The change of the sound pressure level as the distance increases along the right direction is greater than the left direction. Moreover, in Figures 25 and 26, it can be noted how change the sound pressure level as the distance increases; the sound pressure level increases. This behaviour is due to sound reflections on the steps. Figure 27 shows the impulse response trend, with the sound source is on the stage, while Figure 28 shows the impulse response when the sound source is in the orchestra and receiving microphone point is on the octave step of the cavea (position at about halfway of the cavea). For both configurations the impulse response is composed of a succession of reflections: the first due to the contribution of direct sound, the second due to reflection on the ground, while the latter are multiple reflections due to the presence of the steps that contribute to the reinforcement of the direct sound.
Figure 27. Impulse response, with the sound on the stage
and receiving microphone point in the cavea.
Figure 28. Impulse response, with the sound source in the
orchestra and receiving microphone point in the cavea. With the sound source on the orchestra, Figure 29 shows the value of sound pressure level (Lp) in dBA for six different microphone points in the cavea at the sixth row. While Figure 30 shows the value of sound pressure level (Lp) in dBA for six different microphone points in the cavea at the fourteenth row. The value of the sound
pressure level (Lp) is higher on the right part of the cavea, while on the left part the sound pressure level (Lp) value is inferior. The acoustic measurements confirm that the theatre is not symmetric, the sound levels on the right side of the cavea are greater than for the left. This is due to the contribution of the sound reflections of the exterior walls of the church on the right side of the cavea. Regarding the extremely low measured average values of the reverberation time, it is possible to notice how due to the absence of the scene wall and therefore an important reflecting surface (the average measured time is 0.80 s, unlike the average times of the baroque theatres that are of 1.5 s).
Figure 29. Sound pressure level (dBA) in the cavea, row
sixth, when sound source is in the orchestra.
Figure 30. Sound pressure level (dBA) in the cavea, row
XIV, when sound source is in the orchestra.
There is an increase of the frequency of 500 Hz observing the trend of the average values of reverberation time T30.
This increase is due to the reflections of the sound waves on the staircases that, for their dimensions (0.40 m of height and 0.70 m of depth), allow for a greater reflection of the sound just at the frequency of 500 Hz. The acoustic measurements have highlighted how the legendary “good acoustics” of the theatres of the Greek and Roman age were not due only to the absence of any background noises and the features of the building materials (strongly reflecting surfaces), but also to the layout of the staircases (12, 13, 14, 15, 16). These being of regular shape and set at a constant pace, react as spreading surfaces, and therefore contribute to a uniform propagation of the sound in the theatre, improving its acoustics. The EDT values are lower than those obtained from T30, since the absence of
reflective surfaces does not provide adequate values for this parameter, whereas the standard deviation values are higher than T30, with this being due to the EDT measured
values varying significantly from point to point. The average D50 values are near the unit value, with the theatre
4. CONCLUSIONS
The Roman theatre of Benevento can be considered one of the best preserved theatres existing in Italy. One of the advantages of the theatre is the fact that although it is located in the heart of the city it is far from the traffic lines, so background noise levels inside the theatre are very low. The analysis of the acoustic measurements give us that the reverberation times do not exceed 1.0 second. In the theatre there are not reflective surfaces that give a good acoustics for musical representations. In the current configuration, it can be used optimally for prose and acting performances, but not for performing lyric or symphonic music. The optimum listening conditions for this configuration are the first rows of the cavea near the orchestra pit. For a better sound perception by listeners with singers and actors without amplification, such as lyricism, prose, and comedies, it would be desirable for the actors to stand in the orchestra pit and not on the stage, as is the case today. For better acoustic performance, it might be hypothesized to install PVC rigid panels at a height equal to that of the columns on the stage and cover part of the stage with a roof of the same size as the stage so as to recover the sound that would otherwise go scattered through the open space of the stage wall.
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